Continuous hollow casting



Sepf- 30, 1958 R. K. PADDocK l 2,853,754

CONTINUOUS HOLLOW CASTING 'Y Filed July 17, 1957 14 i? y w Wa/er UnitedStates Patent() v g Y 2,853,754 I CONTINUOUS HOLLOW CASTING Richard K.Paddock, Edwardsville, Ill., assignor to The Dow Chemical Company,Midland, Mich., a corporation of Delaware Application July 17, 1957,Serial No. 67.2,492

Claims. (Cl. 22-200.1)

The invention relates to casting hollow ingot continuously of amagnesium-base alloy and is particularly concerned with ingot ofcylindrical form with a longitudinal central cylindrical passageway fromend to end as in a thick walled tubular ingot.

Magnesium-base alloys, generally containing over 85 percent ofmagnesium, particularly those containing one or more alloying metals, e.g. aluminum, manganese, zinc, and zirconium, as in alloys having theASTM Designations AZ31, AZl, ZK60, and the like, have been castsuccessfully continuously in open ended chill molds into ingot when ofsolid form. On the `other handdiiculties arise when an attempt is madeto apply known methods of continuous casting of hollow or tubular ingotof these alloys in similar molds. Among the diiculties observed are thatthe surface of the ingot is rough and uneven, the inside wall isoftentimes cracked, crystal structure is not uniform, and the metal isexcessively porous. Cylindrical ingot having a longitudinal cylindricalpassageway from end to end, that is tubular ingot, of magnesium-basealloy is used in the manufacture of tubular goods by die expressing theingot using a central mandrel located in the passageway to form the boreof the tube as it extrudes. u

Because sound hollow or tubular ingot suitable for this use ofmagnesium-base alloy cannot be produced by the known continuous castingmethods recourse is had to the use of a batch casting process for makingthe ingot. This is laborious and time-consuming. Accordingly, it is anobject of the invention to provide a continuous casting method whichovercomes these drawbacks. Other objects and advantages will appear asthe description of the invention proceeds.

According to the invention, smooth tubular non-porous ingot free fromshrink or other forms of cracks which form on applying conventionalmethods of continuous casting of hollow ingot, is obtained by deliveringat a particular rate a continuous ow of the molten alloy to be cast inthe annular space between a cooled cylindrical open ended verticallydisposed mold and a cooled mandrel therein vertically disposed, themolten metal being at usual casting temperature, e. g. 1200 F. to 1400F., depending upon the composition of the alloy. tion to feeding themolten metal into the annular space at a particular rate, the feeding isconducted in a manner such that the molten metal is introduced beneaththe surface of the molten metal already in the mold beforesolidification and distributed around the annulus. While so controllingthe feed of molten metal to the mold, heat is abstracted from theso-introduced metal so as to bring about solidication. The abstractionof heat from the metal is carried out through the mold and mandrel in amanner such that there is producedfinthe annulus a particular form ofinterface between the molten metal in the mold and the solidiedmetalfv'Ihe forml of the interface in the annulus between the moldand-rvmandrel, 'yiewed in vertical cross section, is a Vextending aroundPatented Sept. 30, 1958 ICC the mandrel with the bottom of the Vpointing downwardly. In carrying out the heat abstraction, it has beendiscovered that the location of the bottom of the V, with reference tothe mandrel, canube varied according to the amount of cooling appliedto'both the mold and mandrel and that the location of the bottom of theV can be used as a guide to the production of sound ingot. By so coolingthe mandrel andmold that the bottom of the V is spaced from the mandrela distance, measured horizontally, of from Ms to 1%; of the thickness ofthe annulus of metal sound ingot is obtained.

The invention may 'be` further understood and explained by reference tothe accompanying drawing showing a preferred embodiment of apparatussuitable for carrying out the invention. l

In the said drawing,

, Fig. 1 is a vertical section of the casting operation.

Fig. 2 is an enlarged fragmentary view of Fig. 1 showing the annulus invertical section and the form and location therein of the interfacebetween the molten and solidiied metal.

Referring to` the drawing in detail, there is shown a verticallydisposed open ended cylindrical mold 1 provided with a rim2 by which itmay be supported in a suitable frame (not shown). Surrounding theoutside of the mold a short distance (e. g. 2 inches) from it are rings3 and 4' of perforated pipe for cooling Water, the perforations 5 facingdownwardly and towardthe outside wall 6 of the mold. A similar ring 7 ofperforated pipe is provided below the mold for directing cooling water(optionally air may be used) against the. ingot as it emerges from themoldas will be described later. These rings are connected throughcontrol valves 8, 9, and 10, respectively, to a source (not shown) ofcooling water. Vertically disposed inside the mold along the centralvertical axis thereof is a mandrel 11. This is in the formof a hollowcylinder as shown closed at the top and bottom with end members 12,and13, respectively. Through the top end member extends a cooling waterinlet pipe 14 connected through a control valve 15 to the water source.The lower end of pipe 14 terminates in a water distributing vcylindricalbox 16. The vertical wall 17 of the box is perforated with a series ofholes 18 evenly spaced around Athe box. An outlet 19 is provided in theendmember 12 for the spent cooling water from the mandrel. The upper end12 of the mandrel is at substantiallyk the same height as the rim 2 ofthe mold while the lower end 13 extends downwardly substantially thesame distance as the mold.

Within the annular space 20 between the mold 1 and mandrel 11 at theupper end of the mold is a ring shaped trough 21 open at the top 22. Thetrough 21 is connected to and supported by the bifurcated feed pipe 23leading from the header box 24 which is connected to the molten metalsupply line 25 through a valve 26 leading from'a source (not shown) ofmolten alloy to be cast.

v In operation a dummy `block (not shown) `of some kind, such as aprecast` portionY of ingot, is inserted into the bottom of the mold 1 inorder to form a seal between the mold and mandrel to hold molten metalin the mold when rst starting the apparatus. With the dummy block inplace, some cooling water is directed against the mold by partiallyopening valves 8 and 9 and the mandrel 11 is cooled more or less bypartially opening valve 15. The dummy block also may be cooled to someextent by opening partially valve 10 or by directing air against it.Molten magnesium-base valloy is introduced into the annular space v20 bysuitably opening valve 26.

n The level of the molten metal inthe mold is allowed the apparatusshowing to rise until lnear the rim as shown and then the dummy block islowered while maintaining a ow of alloy into the mold at a rate whichkeeps the mold more or less full, the lowering. beingata rate of about 2to `4. inches per minute.. As thelowering proceeds, molten. metalsolidi'es against themold wall, againstthemandrel, and dummy block.Themetal so-solidifled is lowered from the mold at the desired rate andthedummyblock is discarded. The introduction of molten alloy into themold and lowering of the resulting cast.` ingot is con.- tinued asdesired.

The solidiication process which produces the ingot gives rise toanint'erfa'ce between the liquid metal in the upper part of the mold andmetalalready solidified from the molten state and seals. the moldagainst leakage of molten metal. .A form of. interface which can beproducedV when lappropriateV operating conditions are obtained inaccordance with the invention is shown. at 27. As the casting proceeds,cast ingotisf moved from the bottom of the mold at a rate to maintainthetop'` of the interface submerged in the moltenmetal in the mold.

As shown in Fig. 1 and in greater detail in Fig. 2, the lowermostportion28 .of `the interface together with Vthe portions 29. and 30- adjacentto the mandrel and mold wall, respectively, have generally a V shapeV asaforementioned. This shape is maintained by appropriately cooling boththe .mandrel and the mold wall.

The desiredjingot 31 is obtained when the lowermost portion28 or V ofthe' interface is within a certain distance measured horizontally of themandrel. As shown in Fig. 2, the distance A represents the distancebetween the lowermost" portion of the interface 27 from .the mandrel 11and is used as the control for the method of the invention. In order toobtain sound crack-free smooth non-porous uniformly crystalline ingotcontinuously, the distance A, it-has been discovered, must 'lie betweenthe distances Band C where B is 1A; and C is 2%; of the thicknessV ofthe annulus 20.

When steady operation is obtained, that is, when ingot 31 is emergingfrom the mold at the rate of about 2 to 4 inches per minute and moltenmetal is introduced at a rate corresponding to.this,.the cooling waterilow through the mandrel ismaintained at a rate such that the distance Ais kept within the limits B and C as shown; This is. accomplished byadjusting the flow of cooling water particularly tothe mandrel. Theposition of the lowermost portion of the interface is ascertained by aprod which may consist of a steel rod 32. This ismanipulated by handt asby inserting it into the molten metal and, feeling for the position of28. By holding the prod vertical when. its lower end is at the bottomofthe V, as shown in Fig. 2, the distance A lis readily obtained bymeasuring the distance Af.

It is manifest that the position of 2S cany be moved toward either themandrell or the mold by controlling the f flow of cooling water to theseparts of the apparatus. Substantially more cooling must bey applied tothe mold wall and ingotsurface than to the mandrel in order to maintain28. within the limits found..to produce sound ingot. When the positionofY 28 has' been brought within the prescribed limits and steadyoperation obtains the prodis removed; In this connection, it is foundthat the temperatureiof the cooling' water. leaving the mandrel can. beused as -a reliable indication of the proper position. of the lowermostportion of the interface toproduce soundingot. More particularly, it hasbeen found, using cooling waterof the usual range of temperature ofpotable water, that when a steady state of casting obtains, as whencooling water is being applied to the outside of the mold, the outsideof the ingot, .and-.the inside( of the mandrel,` the desired position ofthe bottom of the lVY isyobtained when the mandrel cooling water exit'temperature isbetween about 140 and 170 F.

It will bey observedn that in carrying ,out` the method, the moltenmetall Yin the mold isal'ways annular in shape 4 because the upper endof the mandrel extends above the working level of the molten metal inthe mold as shown.

The following examples, runs 1 to 5,- inclusive, the pertinent data ofwhich are set forth in the table, are illustrative of the practice ofthe invention. Two runs, 5 and 6, outside the range of the operatingconditions for the invention are detailed for comparison.

Water Rates, Y Casting Gal/Min. Temp., Ingot Rate, F., of Mandrel.Quality Run Alloy Inches Water Diameter, 'of No. Desig- Per to toLeaving Inches Ingot nation Minute outside .ingot Mandrel of below mold1mold 3. 2 14 5 165 4. 75 good. 2. 8 16 air 165 4. 75 good. 3. 25 16 5165 3. 25 good. 2. 75 12 5 143 2. 25 good. 4.0 .11 5 143 10.5 good. 2.514 Y 5 l 185 4. 75 bail. 4.0 14` 5 130 4. 75 bad.

1 O. D. of mold 16.1875". Molten alloy input temperature1275J F. forZKeo, 13oo F. for A231.

Runs 6 and 7 are blanks for comparison. Good means the ingot was smooth,free from cracks, of uniform crystal structure, non-porous. Bad meansthe ingot was roughv cracked, non-uniform in crystal structure andporous. u l

Referring to the table, runs l to 5, inclusive, in which the mandrelcooling Water exit temperature was 1n the range of. 143 to 165 F.produced good smooth nonporous uniformlyV crystalline ingot; whereaswhen the mandrel cooling water exit temperature was lallowed to goashigh as 185 F. or as low as 130 F. cracked, rough, porous, irregularlycrystalline ingot resulted. Concernitantly, the lowermost portion of theinterface, i. e., the bottom of the V' as located by prod 32, wasshifted from Y the limits between B and C in runs 6 and 7; while duringthe production of sound ingot as in runs l tov 5 the posi- 1 tion of thebottom of the V was within the range of ls to 3/8 of the thickness ofthe annulus. The water used for cooling had a temperature in the rangeof 50 to I claim:

1. The method of Vproducing a sound tubular, heavy walled ingotcontinuously of a magnesium-base alloy containing at least percent ofmagnesium, which comprises delivering the molten magnesium-base alloy toa vertically disposed open ended cooled mold having a centrally disposedmandrel therein at a rate suicient to till the mold to a depth of from 2to 4 inches per minute when closed at the bottom coolingthe outside ofthe mold and the inside of the mandrel at a rate such that the lowermostportion of the resulting interface between the molten and solidied metalin the mold is at a distance from the mandrel of l/s to 3/8 of the `wallthickness of the ingot while withdrawing ingot from below thev mold at arate suicient to maintain the mold sealed against leakage of moltenmetal and the uppermost portion of the interface below the upper surfaceof the molten metal in the mold.

2. The method according to claim l in which the outside of the mold andthe inside of the mandrel are cooled with water having a temperaturebetween50 and 80 F. at a rate such that'the exit temperature of theWater from the mandrel is between and 170 F.

3. The method according to claim 2 in which the molten magnesium-basealloy is delivered to the mold at a temperature between 1200 and 1400 F.

4. The method according to claim 3 in whichthe molten magnesium-basealloy is delivered beneath the surface of the molten magnesium-basealloy in the mold.

5. In a method of producing sound tubular heavy walled ingotcontinuously of a magnesium-base alloy containing atleast 85 percent ofmagnesium, the steps which consist in delivering the moltenmagnesium-base alloy at atemperature of 1200l to 1400 FQ toa verticallydisposed open ended cooled mold having a centrally disposed cooledmandrel therein at a rate sucient to ll tance equal to from 1A; to ofthe wall thickness of the mold to a depth of from 2 to 4 inches perminute the ingot, the delivery of the molten alloy being beneath whenclosed at the bottom, cooling the outside of the the surface of themolten alloy in the mold. mold and the inside of the mandrel with waterhaving a temperature of from 50 to 80 F. at 'a rate such that 5'References Cited in the me 0f this Patent the exit temperature of thewater from the mandrel is UNITED STATES PATENTS between 140 to 170 F.whereby the lowermost portion 2,225,415 Junghans Dec. 17, 1940 of theInterface between the molten metal and the so11d1- 2,473,221 Rossi June14 1949 ed metal in the mold is spaced from the mandrel a dis-

1. THE METHOD OF PRODUCING A SOUND TUBULAR HEAVY WALLED INGOTCONTINUOUSLY OF A MAGNESIUM, WHICH COMPRISES TAINING AT LEAST 85 PERCENTOF MAGNESIUM, WHICH COMPRISES DELIVERING THE MOLTEN MAGNESIUM-BASE ALLOYTO A VERTICALLY DISPOSED OPEN ENDED COOLED MOLD HAVING A CENTRALLYDISPOSED MANDREL THEREIN AT A RATE SUFFICIENT TO FILL THE MOLD TO ADEPTH OF FROM 2 TO 4 INCHES PER MINUTE WHEN CLOSED AT THE BOTTOM COOLINGTHE OUTSIDE OF THE MOLD AND THE INSIDE OF THE MANDREL AT A RATE SUCHTHAT THE LOWERMOST PORTION OF THE RESULTING INTERFACE BETWEEN THE MOLTENAND SOLIDIFIED METAL IN THE MOLD IS AT A DISTANCE FROM THE MANDREL OF1/8 TO 3/8 OF THE WALL THICKNESS OF THE INGOT WHILE WITHDRAWING INGOTFROM BELOW THE MOLD AT A RATE SUFFICIENT TO MAINTAIN THE MOLD SEALEDAGAINST LEAKAGE OF MOLTEN METAL AND THE UPPERMOST PORTION OF THEINTERFACE BELOW THE UPPER SURFACE OF THE MOLTEN METAL IN THE MOLD.